Computed tomographic evaluation of the proximal femur: A predictive classification in displaced femoral neck fracture management

BACKGROUND: Femoral neck fracture is truly an enigma due to the high incidence of avascular necrosis and nonunion. Different methods have been described to determine the size of the femoral head fragment, as a small head has been said to be associated with poor outcome and nonunion due to inadequate implant purchase in the proximal fragment. These methods were two dimensional and were affected by radiography techniques, therefore did not determine true head size. Computed tomography (CT) is an important option to measure true head size as images can be obtained in three dimensions. Henceforth, we subjected patients to CT scan of hip in cases with displaced fracture neck of femur. The study aims to define the term small head or inadequate size femoral head” objectively for its prognostic significance. MATERIALS AND METHODS: 70 cases of displaced femoral neck fractures underwent CT scan preoperatively for proximal femoral geometric measurements of both hips. Dual energy X-ray absorptiometry scan was done in all cases. Patients were treated with either intertrochanteric osteotomy or lag screw osteosynthesis based on the size of the head fragment on plain radiographs. RESULTS: The average femoral head fragment volume was 57 cu cm (range 28.3-84.91 cu cm; standard deviation 14 cu cm). Proximal fragment volume of >43 cu cm was termed adequate size (type I) and of ≤43 cu cm as small femoral head (type II). Fractures which united (n = 54) had a relatively large average head size (59 cu cm) when compared to fractures that did not (n = 16), which had a small average head size (49 cu cm) and this difference was statistically significant. In type I fractures union rate was comparable in both osteotomy and lag screw groups (P > 0.05). Lag screw fixation failed invariably, while osteotomy showed good results in type II fractures (P < 0.05). CONCLUSION: Computed tomography scan of the proximal femur is advisable for measuring true size of head fragment. An objective classification based on the femoral head size (type I and type II) is proposed. Osteosynthesis should be the preferred method of treatment in type I and osteotomy or prosthetic replacement is the method of choice for type II femoral neck fractures.